1. Field of the Invention
The invention relates generally to lignin recovery processes and, more specifically, to methods for recovering lignin through neutralization of alkaline lignin solutions. In particular, the invention relates to an electrochemical method whereby both lignin and alkali are recovered in anode and cathode chambers, respectively, of one or more electrochemical cells. The invention is ideally suited for recovering lignin from the alkaline extract of a cellulose process.
2. Background of the Invention
In the production of cellulose, considerable amounts of lignin-containing extracts are obtained which have heretofore represented a waste product. As the direct discharge of the extracts into waterways is no longer possible at the present time, the extracts have been subjected to a concentration process, and the solid materials obtained usually burned. The methods used in the process are expensive and have been employed only to obtain purified water and solids separated therefrom. The water may then be returned to the waterways. The process is not only expensive, but the lignin contained in the solids is destroyed. The extracts are usually designated waste liquors.
A method for precipitating lignin from an alkaline solution is known, whereby the solution is neutralized by the introduction of acids, but a subsequent recovery of the lye is not possible or is highly involved and expensive. Furthermore, the material precipitated in this manner is contaminated by mineral salts. Alkaline liquors may be neutralized, for example, by the introduction of carbon dioxide, and the carbonate so-formed, causticized with calcium oxide. There remains, however, a need in the art for an inexpensive method for recovering both lignin and alkali from an alkaline lignin solution.